Experimental Observation of a Heavy ParticleJ

Abstract

We report the observation of a heavy particle $J$, with mass $m=3.1\mathrm{}$ GeV and width approximately zero. The observation was made from the reaction $p+\mathrm{Be}\to e^{+}+e^{-}+x$ by measuring the $e^{+}{e}^{-}$ mass spectrum with a precise pair spectrometer at the Brookhaven National Laboratory's 30-GeV alternating-gradient synchrotron.